The Wardha bypass came up first - sometime in the late 1960's and early 1970's. The halt was eliminated and trains like GT, MAdras Delhi Janata and the Southern express started bypassing Wardha immediately.
The Kazipet bypass was also ready by the early 1970's. But all the Delhi bound trains from the south had through coaches to SC/HYB that had to be attached detached at some place. Since Kazipet was already a junction with a large yard and all other facilities, the trains continued to run through Kazipet, reversing there.
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Tamil Nadu express was the first train to start bypassing Kazipet regularly. The GT continued to reverse at KZJ until 1987 or so.